What is the fine-grained topic of the following text: Penson director Thomas R. Johnson resigns citing: "Mr. Johnson's position as chief executive officer of Call Now, Inc a holder of a portion of the Retama related collateral, both Mr. Johnson and the Company felt it appropriate for him to resign his position at this time." Only return the topic.
Thomas R. Johnson's resignation from Penson due to his role at Call Now, Inc.